JPS5852247B2 - Overcurrent limit circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an overcurrent limiting circuit using an on-off switching element.

Generally, to limit overcurrent, a method is often used in which a current switch element is operated based on an overcurrent detection signal.

In this case, the overcurrent is detected at two levels, the switching element is turned off when the current is detected to have reached a certain level, and the switching element is then turned off when the current is detected to have decreased to a small level. In many cases, the switch element is turned on again.

In the case of such a conventional method, current detection requires two values, and a hysteresis processing circuit as described above is also required, resulting in a complicated circuit.

The present invention aims to enable current limiting with a relatively simple circuit system having substantially the same function as the conventional system, and the details thereof will be explained below with reference to examples.

FIG. 1 shows an embodiment of the present invention, and FIG. 2 shows its operation.

In FIG. 1, 1 is a power supply, 2 is a load, 3 is a current switch element, 4 is a driver for 3, or 5 is a current detection resistor.

After the current detection signal from 5 is amplified by an amplifier 6, it is compared with an overcurrent setting value by a conhaler tough.

That is, 7 drives the driver 4 via the AND gate 9 as a binary signal that is on when the load current i is less than the set value and off when it is more than the set value.

The output of 7 is further configured to trigger a monostable multi-by-break 8 .

In other words, the moment the output of 7 turns off, 8 starts operating,
The driver 4 is turned off for a set period of time regardless of the output state of the driver 7.

Their operating states are as shown in FIG.

Load current i is set value i. At the moment when 7 is reached, the output of 7 is turned off.

At the same time, 8 is triggered and its output is also turned off.

After the turn-off time of current switch 3 has elapsed, the current begins to decrease, and the output of 7 turns on again, but the output of 8 remains unchanged for a certain period of time T.

remains off during this period, and the current also continues to decrease during this period.

After To has elapsed, the current switch 3 is turned on again, and the same operation is repeated.

However, T. If the output of 7 is off even after the elapse of time, the current switch 3 naturally remains off.

In this way, since the upper limit of the operating frequency of the switch circuit is determined by the time constant of the monostable multi-bibreak, it is possible to prevent power loss due to the switch circuit and burnout caused by this.

Furthermore, within this frequency limit range, by changing the time constant of the monostable multi-bibreak, the magnitude of the load current pulsation can be set arbitrarily, as if the load current were detected at two levels. has the same effect.

As described above, according to the present invention, current limitation with little loss is possible with a relatively simple circuit configuration, which is industrially highly effective.

It is clear that the principles of the present invention can be applied regardless of the type of switch circuit or the configuration of the power supply or load.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment according to the present invention, and FIG. 2 is an explanatory diagram of its operation.

Claims (1)

[Claims] 1. In an overcurrent limiting circuit that is composed of a load, a power source that supplies power to the load, and a switch circuit that controls the supply of power, and that limits the current flowing to the load by the on/off operation of the switch circuit, the current a comparison means for comparing the current with a set value; a signal generation means for generating a signal indicating a predetermined time interval from when the current exceeds the set value; and an output of the comparison means and an output of the signal generation means. an overcurrent limiting circuit comprising: control means for controlling on/off operations of the switch circuit in accordance with the above, and wherein the control means turns off the switch circuit at least during the predetermined time interval.